1. Field of the Invention
The present invention relates to a headlight for a vehicle, and more particularly, to a headlight for a vehicle having a centralized light source.
2. Description of Related Art
Recently, a discharge-tube-type headlight system in combination with a control circuit has been developed. Since the control circuit is considerably expensive, a single centralized discharge-tube is disposed in a portion of the vehicle and light beams are introduced through fiber optic cables to portions where right and left head lights are located. For instance, Japanese Patent Unexamined Publication Hei 6-68702, which was filed by the assignee of this application, discloses an example. The headlight system includes a centralized light source 1 disposed in a front central portion of the vehicle and left and right head lights L and R. The centralized light source 1 has a generally cylindrical casing in which a discharge tube 1a as a linear light source 1 at an axially central portion. Reference characters FL and FR indicate left and right wheels.
The left head light L is composed of a lens unit 2 disposed in a front left portion of the vehicle and a fiberoptic cable 3 which connects the centralized light source 1 and the lens unit 2. The right head lamp R is composed of a lens unit 4 disposed in a front right portion of the vehicle and a fiberoptic cable 5 which connects the centralized light source 1 and the lens unit 4.
When the lens units and the fiberoptic cables are connected, the fiberoptic cables have to be bent very carefully in order to minimize the light transmission loss. In order to dispose the fiberoptic cable without paying the above attention into account, a curved light conducting portion is formed in the lens unit as disclosed in U.S. Pat. No. 5,436,806 filed by the same assignee. FIG. 7 is a perspective view illustrating such lens unit, and FIG. 8 is a schematic plan view thereof.
In the lens unit shown in FIGS. 7 and 8, the lens unit is composed of two kinds of lens members having different lens characteristics. A first lens member 30c has a lens function only in the vertical direction and forms a flat zone illumination. A second lens member 40 is a common omnidirectional lens and, therefore, the light beams are magnified and focused to an inverted original image, thereby forming a hot zone illumination which illuminates comparatively narrow area brightly. Shades 20 are disposed between the first and second lens members 30c and 40 so that glaring light beams against passing or meeting vehicles can be cut, thereby forming the low beam illumination of the headlight. The second lens member 40 for the hot zone illumination has a reflecting surface R which is beveled at an angle of 45 degree with respect to an incident axis X--X and located opposite the incident portion. Therefore, the incident light beams from the fiberoptic cable 10 are totally reflected by the reflecting surface R, turned by 90 degree and emitted from a light emitting surface 46.
The first lens 30c for the flat zone illumination has a 90-degree-curved-portion 30cR so that light beams are emitted therefrom at an angle of 90 degree from the direction of the incident light beams. The entire periphery of the 90-degree-curved-portion 30cR is exposed to material having a small refracting index such as air, and the sorrounding surfaces of the 90-degree-curved-portion totally reflect all the incident light beams to emit all incident beams from the light emitting surface 36c.
However, the above described lens having the 90-degree-curved-portion 30cR can not provide a uniform and sufficient illumination zones due to geometric form of the 90-degree-curved-portion as shown in FIG. 9 which shows illumination characteristics on a screen located 10 m in front of the lens 30c having the 90-degree curved portion. A curved line A represents a zone where the illuminance is 60 lux, a curved line B represents a zone where the luminance is 40 lux and a curved line C represents a zone where the luminance is 20 lux. The zone C is 10 degree high (in a V--V direction) and 120 degree wide (in a H--H direction).